Many portable electronic devices include displays for displaying various types of images. Examples of such displays include electrowetting displays (EWDs), liquid crystal displays (LCDs), electrophoretic displays (EPDs), light emitting diode displays (LED displays), etc. In EWD applications, an addressing scheme is utilized to drive the pixels of the EWD. Generally, one of the points of emphasis for EWD applications is low power design since in today's applications EWDs are often intended to be used in mobile and portable media devices.
An input video or data-stream generally represents a sequence of pixel display values, grouped per line; a sequence of lines, grouped per frame; and a sequence of frames defining a frame sequence. When such a data stream is to be reproduced on an active matrix EWD, a timing controller and display drivers are used to process the incoming data-stream to control the actual pixels of the EWD. A specific addressing scheme is used by the timing controller to timely control row and column drivers of the EWD. The purpose of an addressing scheme is to set (or maintain) the state of a pixel. The addressing scheme drives an active matrix transistor array and provides analog voltages to individual pixels of the EWD. These voltages modulate the luminance transmission and/or reflectivity of the pixels of the EWD. The pixels are grouped per row and when a row is addressed, voltages of a complete row are stored as charge on corresponding pixel capacitors. As the display-data is repeatedly updated, still and moving images can be reproduced by the EWD.
Once a pixel is set to a particular display state, however, over time, the pixel's brightness or luminance will gradually diminish. Leakage of charge from the pixel's capacitor, for example, can reduce pixel luminance. Such leakage may result from current flow through active matrix switches and dielectric materials. Additionally, even without such a reduction in pixel capacitor charge, the fluids contained within the pixel can experience a phenomena referred to as backflow, in which the fluids tend to return to their original resting positions (i.e., with no charge applied to the pixel's capacitor). This also can cause a reduction in pixel luminance. In an attempt to mitigate these problems, the display's timing controller may periodically reset each pixel. If the pixels are reset very frequently, however, the image quality can be reduced and the power consumption may increase. Accordingly, in most displays the frequency with which pixels are reset is reduced. But, at a sufficiently low frequency, the pulses may be noticed by an observer as periodic reductions in brightness. These temporary reductions of display device luminance may cause visual image artifacts.